Dental caries is one of the two major dental diseases including a periodontal disease, and about a half of tooth loss is due to dental caries. Similarly to a cold, dental caries is commonly seen in any generation. Especially children readily suffer from dental caries for several years after tooth eruption, showing low calcification, and dental caries is often seen in people under 20. Dental pulp, a so-called nerve of a tooth, has functions of blocking external stimulus by tooth (dentin) formation potential and inhibiting development of dental caries and tooth fracture by sense. Dental pulp also has an important function in tooth survival by metabolic and immune systems.
With a current pulpectomy technique, complete pulpectomy and root canal filling are almost impossible, and abnormality occurs in apical areas (periapical periodontitis) in a later stage, leading to the necessity of an infected root canal treatment in many cases. In such cases, a single chair time is longer than that in a dental caries treatment, and a long-term treatment is often needed. It is also possible that symptoms such as drainage from the apical foramen or pain are not improved, which leads to a tooth loss by tooth extraction. Tooth pain causes severe difficulties in daily life, and reduces social productivity. As dental caries grows to dental pulp and further to bone in the apical area to finally cause tooth extraction, mental and economic burdens of patients increase, and declined functions of mouth and occlusion cause motor dysfunction, autonomic imbalance, and problems in pronunciation and aesthetics.
In conventional dental caries treatments, it is necessary to physically completely remove dental caries (softened dentin) in order to completely kill bacteria which have invaded deep parts of dentin tubules. This removal increases the possibility of excessive loss of dentin, leading to exposure of dental pulp.
There is also a root canal treatment known as the treatment of removing a portion suffering from dental caries and cleaning and disinfecting the inside of a root canal. In the root canal treatment, a portion suffering from dental caries is first removed, and then enamel and dentin are removed as necessary in order to easily perform the root canal treatment. Next, after the depth of the root canal has been precisely measured with, for example, the sense of fingers, X-ray photographs, or an electronic root canal length measurement, dental pulp or dentin infected by bacteria is removed with a tool such as a reamer or a file. Thereafter, a predetermined drug is placed in the root canal from which dental pulp has been removed, and the root canal is irrigated, cleaned, and disinfected with a tool such as a broach. Lastly, the root canal is filled with gutta-percha, thus finishing the root canal treatment.
The root canal treatment is classified into a pulpectomy treatment and an infected root canal treatment. If dental caries is deep enough to reach dental pulp, the pulpectomy treatment is generally employed. The pulpectomy treatment is a removal of dental pulp inside a tooth. Dental pulp which is or might be infected is thoroughly removed by the pulpectomy treatment. Thus, it is possible to prevent inflammation from reaching periodontal tissue, and a tooth affected by caries is made harmless to periodontal tissue, thereby recovering chewing ability.
An infected root canal refers to a state in which dental caries develops to dental pulp to cause necrosis of the dental pulp due to infection or a state in which insufficient filling of the root canal causes infection of the inside of the root canal. The infected root canal treatment is employed in these cases. In a severely infected root canal, an apical periodontal cyst or a fistula (a passageway through which pus accumulated around teeth is drained) is created. In the case of the infected root canal, it is necessary to clean and disinfect the inside of the root canal before filling the root canal. If the root canal was insufficiently filled with a root canal filler in the past, the root canal filler is temporarily removed so that the inside of the root canal is cleaned and disinfected again, and then the root canal is filled to the root apex.
However, it is difficult to observe the structure directly in the root canal, and the shape of the root canal is complex such that the root canal is curved or blocked and has a large number of accessory canals, lateral branches, or the like. Thus, it is very difficult to remove bacteria completely in the root canal. In addition, if the root canal is filled with a filler or covered with a crown with bacteria being left in the root canal, the bacteria will proliferate in the root canal later in some cases, leading to the necessity of an additional root canal treatment. In a case where an additional root canal treatment is required later, the filling or the crown used in the previous treatment needs to be replaced with new one, and further, the possibility of tooth extraction might arise. If the treatment is excessively localized on removal of residual bacteria in the root canal, dentin can be excessively removed, which lead to better the patients' quality of life (QOL). Since the shape of a root canal is complex as described above, the root canal treatment (treatment of dental nerves and roots) is very difficult.
Patent Document 1 describes a system for irrigation of a tooth root canal using ultrasonic energy. The system for irrigation of a tooth root canal includes an injection tube having a flexible distal end configured to be inserted into a root canal. This injection tube is inserted into the root canal so that a fluid having ultrasonic energy superimposed thereon is forced into the root canal, thus performing irrigation.
In the system for irrigation of a tooth root canal described in Patent Document 1, however, the fluid having ultrasonic energy superimposed thereof is merely released to the apical area of the root canal, and it is difficult to irrigate minute portions of the root canal with a complex shape.
Patent Document 2 describes a tooth root canal treatment system including a motor for rotatably driving a root canal drill. Driving of this motor is controlled in the following manner. In inserting the root canal drill into a root canal with the motor rotated in the reverse direction to the rotation direction of the root canal drill for cutting the root canal, rotation in the reverse direction of the root canal drill is maintained until an electronic root-canal-length measurement detects that the distal end of the root canal drill reaches a predetermined reference position. When the electronic root-canal-length measurement detects that the distal end of the root canal drill has reached the reference position, the rotation in the reverse direction of the root canal drill is stopped.
In the tooth root canal treatment system described in Patent Document 2, the root canal drill can be rotated in the reverse direction to the direction of rotation for cutting the root canal. In this system, after the root canal has been drilled and enlarged by rotating the root canal drill in the positive direction, a drug solution is injected into the root canal. Then, the root canal drill is rotated in the reverse direction and inserted into the root canal so that positive rotation of the root canal drill causes small cuttings produced by drilling to be ejected to the proximal end (upstream) of the root canal drill. Accordingly, the above-mentioned insertion with the reverse rotation pushes the drug solution toward the distal end of the root canal drill.
In the tooth root canal treatment system described in Patent Document 2, however, the root canal drill might excessively drill and enlarge the root canal. In addition, although the drug solution is sufficiently injected into the distal end of the root canal drill, the lateral branches of the root canal are not sufficiently taken into consideration, and thus, it is difficult to irrigate minute portions of the complex root canal.
Patent Document 3 describes a dental therapeutic system in which a liquid supply nozzle for supplying a drug solution (a therapeutic solution) or the like and a suction nozzle are inserted into a root canal with the tips thereof positioned at different locations and a drug solution is injected so that the drug solution fully permeates the root canal. If the liquid supply nozzle and the suction nozzle are positioned such that one of these nozzles is located at a portion deeper than the other in the cavity, the treatment solution reaches at least the deep portion in the cavity. Accordingly, a target area is efficiently irrigated.
In the dental therapeutic system described in Patent Document 3, however, since the tip apertures of the liquid supply nozzle and the suction nozzle for the drug solution face the apical area of the root canal, even if the apical area can be irrigated, the other areas are insufficiently irrigated.
Periodontal disease (periodontal disorder) is inflammation of periodontal tissue which supports teeth. Periodontal tissue is a general term including cementum, gingiva, alveolar bone, and periodontium. Periodontal disease is a disease caused by infection with periodontal disease bacteria from so-called gingival sulci (periodontal pockets) between teeth and gingivae. The periodontal disease is broadly classified into gingivitis with no alveolar bone resorption and periodontitis with alveolar bone resorption. In either case, induced inflammation tends to enlarge periodontal pockets.
Oral rinses, dentifrices, and antibiotics, for example, are known as conventional therapeutic drugs for periodontal diseases. Conventional therapeutic methods include brushing with tooth brushes, and dental calculus removal and irrigation performed in dental clinics. However, the use of dentifrices has the possibility of insufficient cleaning of periodontal pockets if brushing is insufficient. In the case of using oral rinses, although the oral rinses spread in the mouth, the drug solution is not effective in some areas such as periodontal pockets. In the case of antibiotics, arrival of medicinal ingredients at inflammated areas such as gingivae takes too much time after administration, and the antibiotics are not effective against all the periodontal disease bacteria. Patent Document 4 proposes an embrocation liquid for periodontal diseases using shellac as a base material in a tooth coating composition. However, disadvantageously, this embrocation liquid cannot be used in periodontal pockets.
Next, hyperesthesia is a disease in which advanced periodontal disease causes transient pain when the surface of exposed dentin is subjected to cold air, cold water, or tactil stimuli, for example. Exposure of dentin is caused by enamel disappearing or gingival retraction, for example. In the exposed dentin, mechanical wearing or elution of lime due to action of acid or the like forms openings in dentin tubules through which physicochemical stimuli are transmitted to dental pulp to stimulate nerves and cause pain.
For hyperesthesia therapy, there is a technique of filling openings in dentin tubules. For example, Patent Document 5 describes a technique in which a tooth is subjected to a treatment using a water-soluble aluminium compound and fluoride. Patent Document 6 shows a technique in which a tooth is subjected to a treatment using a water-soluble aluminium compound, fluoride, and water-soluble calcium. However, disadvantageously, these techniques cannot have drugs easily permeate dentin tubules, and insufficiently fill the dentin tubules.